The primary objective of this research project is to deepen our understanding of platelet metabolism so that the quality of platelets stored in vitro can be further improved for clinical transfusion. Within the project, there are three specific aims. The first specific aim is to more completely define the patterns of substrate selection and metabolite production by platelets. Substrates which will be studied include glucose, pyruvate, amino acids, ketone bodies, and fatty acids. The experiments will be performed on freshly collected platelets in buffer at physiological temperature and on platelets during in vitro long-term storage at 22 degrees C. The levels of activity of crucial enzymes involved in various metabolic pathways will be measured. For the second specific aim, the investigator will evaluate the use of the buffy coat method to prepare platelet concentrates. Paired studies will be performed to determine which component of the new method is responsible for producing the favorable results reported previously. For the third specific aim, megakaryocytes will be isolated from the bone marrow of guinea pigs to study their enzyme levels and patterns of substrate selection and metabolite production. The goal is to compare and contrast the metabolic patterns and enzymatic profiles of megakaryocytes with those of platelets.